The present invention is a process for the preparation of .beta.-cyanoalkylsilanes by contacting a mixture comprising trichlorosilane and an olefinic nitrile with novel phosphinoaliphaticsilane catalysts. The phosphinoaliphaticsilane catalysts are effective in the process as homogeneous catalysts or as supported heterogeneous catalysts. A preferred catalyst for the present process is a phosphinoaliphaticsilane on a solid support. The supported phosphinoaliphaticsilane catalysts have greater activity than the analogous homogeneous catalyst at lower temperatures.
Beta-cyanoalkylsilanes having hydrolyzable chlorines bonded to the silicon atom are useful for the production of polyorganosiloxanes containing the .beta.-cyanoalkyl substituent. The silicon-bonded .beta.-cyanoalkyl substituent is extremely resistant to hydrolysis and cleavage under hot, humid conditions and impart these characteristics to the polyorganosiloxane of which they are a substituent. The presence of the silicon bonded .beta.-cyanoalkyl substituent on polyorganosiloxanes also tends to stabilize the polyorganosiloxanes against swelling induced by liquid hydrocarbons. In addition, .beta.-cyanoalkylsilanes having hydrolyzable chlorines are useful reactive intermediates for forming, for example, gamma-organoaminotrialkoxysilanes which are useful as surface treating agents.
It is known that when trichlorosilane is contacted with an olefinic nitrile, as exemplified by acrylonitrile, at a sufficient temperature a mixture of .alpha.-cyanoalkylsilanes and .beta.-cyanoalkylsilanes is formed. In addition other reactions such as the formation of both silicon and non-silicon-containing complexes, homopolymerization of the starting nitrile, and the disproportionation of the starting silane can occur. The .alpha.-cyanoalkylsilanes are hydrolytically unstable. Therefore, the .beta.-cyanoalkylsilanes generally have more commercial utility than the .alpha.-cyanoalkylsilanes and processes for producing high yields of .beta.-cyanoalkylsilane are desirable.
A number of catalyst have been reported useful in the preparation of .beta.-cyanoalkylsilanes. Saam, U.S. Pat. No. 2,860,153, issued Nov. 11, 1958, described a process for preparing .beta.-cyanoethyltrichlorosilane by heating at a temperature less than 150.degree. C. a mixture of acrylonitrile and trichlorosilane with a catalytic amount of an amine.
Jex et al., U.S. Pat. No. 2,906,764, issued Sep. 29, 1959, describes a process where organosilanes having at least one hydrogen and one hydrolyzable group bonded to silicon are reacted with an alkene nitrile in the presence of a diarylamine catalyst to produce preferentially .beta.-cyanoalkylsilanes.
Jex et al., U.S. Pat. No. 2,907,784, issued Oct. 6, 1959, describes a process where organosilanes having at least one hydrogen and one hydrolyzable group bonded to silicon are reacted with an alkene nitrile in the presence of a trihydrocarbylphosphine catalyst to produce preferentially .beta.-cyanoalkylsilanes.
Bluestein, U.S. Pat. No. 2,971,970, issued Feb. 14, 1961, describes a multiple component catalyst system useful for the production of .beta.-cyanoalkylsilanes by the reaction of alkene nitriles with organosilanes having at least one hydrogen. The catalyst comprises a cuprous compound, a diamine, and a trialkylamine.
Rajkumar et al., Organometallics 8:549 (1989), describes a two-component catalyst effective in hydrosilation of acrylonitrile leading to the .beta.-addition to the double bond of the acrylonitrile. The catalysts consist of cuprous oxide and tetramethylethylenediamine and is reported to be more effective that the previous catalysts taught by Bluestein, U.S. Pat. No. 2,971,970, issued Feb. 14 , 1961. However, the present inventors have found that the process taught by Rajkumer et al. provides a crude mixture which can result in solid residues during subsequent distillation reactions to isolated the desired .beta.-cyanoalkylsilanes. These solid reactants can clog the distillation apparatus making isolation of the desired .beta.-cyanoalkylsilane difficult.
Czakova et al., J. of Molecular Catalysis 11:313 (1981), teaches that certain phosphinoaliphaticsilanes when complexed with rhodium are useful for the hydrogenation of alkenes. These phosphinoaliphaticsilanes complexed with rhodium were also found to be catalytic when supported on silica.
Michalska et al., J. of Molecular Catalysis 11:323 (1981) describes the reaction of hexene-1 with Me.sub.2 PhSiH in the presence of a catalyst comprising a phosphinoaliphaticsilane and rhodium complex on silica.
The present invention is a high-yield process for the preparation of .beta.-cyanoalkylsilanes. The process employs a single component catalyst comprising a phosphinoaliphaticsilane. It is not required that the phosphinoaliphaticsilane be complexed with a metal such as rhodium. No solid residues are generated during subsequent distillation steps to further isolate the .beta.-cyanoalkylsilane. The process can be run as a homogeneous process or as a heterogeneous process where the phosphinoaliphaticsilane is on a solid support.